So can you use electromagnetic fields to repel uncharged objects?

I can see how you can attract conductive objects with an electric field, but I'm wondering if it's actually possible to use some sort of electromagnetic phenomena to repel objects, like in Star Trek, or something

Also, how does a Tokamak fusion reactor keep the plasma in place with magnetic fields? Does the plasma have any net charge, or is it uncharged all in all?

Originally posted by KillaMarcilla I can see how you can attract conductive objects with an electric field, but I'm wondering if it's actually possible to use some sort of electromagnetic phenomena to repel objects, like in Star Trek, or something

Also, how does a Tokamak fusion reactor keep the plasma in place with magnetic fields? Does the plasma have any net charge, or is it uncharged all in all?

The plasma in a Tokamak is a soup of ions without their electrons. So they can be influenced by electrical fields. Acutally, magnetic fields are the main component used to keep the plasma in place. Electrical fields are usually used to heat it up.

of conductive material just by ramping up a magnetic field in a solenoid. But a static electric field just attracts dielectric objects in much the same way that a magnetic field attracts magnetic materials.

Originally posted by KillaMarcilla
Also, how does a Tokamak fusion reactor keep the plasma in place with magnetic fields? Does the plasma have any net charge, or is it uncharged all in all?

plasma is a nickname for ionized gases. for an object to become ionized it must be hyper charged. therefore, yes plasma does have a magnetic charge and that is how the feilds keep it from touching the outer edges.

Originally posted by KillaMarcilla I can see how you can attract conductive objects with an electric field, but I'm wondering if it's actually possible to use some sort of electromagnetic phenomena to repel objects, like in Star Trek, or something

and in answer to your primary question: no, i don't think so. if the object is completly uncharged then definatly no, but you have to remember, at least at the subatomic level, almost everything has a charge. (positive proton, negative electron, ect.) so, who knows?

Re: Re: So can you use electromagnetic fields to repel uncharged objects?

Originally posted by maximus plasma is a nickname for ionized gases. for an object to become ionized it must be hyper charged. therefore, yes plasma does have a magnetic charge and that is how the feilds keep it from touching the outer edges.

You don't 'hyper charge' gases to ionize them -- whatever that means. You heat them up.

Take any neutral material you'd like. Despite the fact that it is outwardly neutral, it is built from charged bits -- positive nuclei and negative electrons. If you apply an external electric field, the material becomes polarised -- the electrons are pushed one direction, and the nuclei the other. The atoms, which are roughly spheric in the absence of an external field, essentially stretch out when a field is applied.

Now say you have an electrode near your material. There is a net polarisation due to the external electric field; one side of the material is more positively charged than the other. Say the electrode is positive, and the strong external field oppositely directed, so that it pushes nuclei toward the electrode.

The result -- you guessed it -- is that the neutral material is indeed repelled by the electrode.

Keep in mind that for many materials, an external field would have to be enormously strong to be able to polarise the atoms very much.

Originally posted by KillaMarcilla [/i
Also, how does a Tokamak fusion reactor keep the plasma in place with magnetic fields? Does the plasma have any net charge, or is it uncharged all in all?

Last things first...
A plasma means separate "free" charged particles.
The plasma in the Tokamak is not charged however
being a plasma means that it has free neucleuses and
electrons that are separate. Now imagine a magnetic
field that is parallel and on all sides of a cross section
of the plasma ring in the Tokomak (the ring and
the field go "into the screen"). If a positive or negative
charge attempts to move somewhere sideways from the ring
axis it is emmidiately affected by the magnetic field
according to the right (right ? ) hand-rule (or
the left if it's an electron) and thus forced to circle
around the axis unable to escape.

Now, if it can gain more transverse energy it can increase
it's radius (you basicly have a Hall current - a torroid
shape current along the axis of the ring). Anyway, the
whole thing is a balance between the EM fields heating
the plasma, the energy from the occasional fusion reactions
and primarily the balance of charges and consequently
energies between the ions and the electrons in the plasma.

In short, it's very complex stuff so we'd better leave
it to those crazy plasma physicts...

Originally posted by KillaMarcilla
I can see how you can attract conductive objects with an electric field, but I'm wondering if it's actually possible to use some sort of electromagnetic phenomena to repel objects, like in Star Trek, or something

Yes, I think. I'm really no expert so I may be making some
mistakes here, so please correct me if I'm wrong.

Light pressure happens because each atom is like a tiny
magnet and it can thus be affected by EM waves.
Another possibility is to accelerate the nucleuses of
the atoms in an ordered fashion in a single direction.
Either way you'll need EM waves at a frequency that
is below the ionisation freq. of the relevant atoms
and you'll need lots of them. Also, the first method
requires huge amounts of energy and is thus hardly practical.
I believe the second possibility may be promising, but
I really honestly know practicly nothing about this.

So you just have to put a strong magnetic field in there, and the plasma's positive cores will go one way, and the electrons will go the other way, but it's all good so long as it doesn't touch anything

I have a job helping a guy who's head of the University of Washington's fusion project, but all I really know is enough to keep away from the equipment, and not to close doors that say not to close them

I'm just redesigning their database, see, since they have a large binder they keep all the data in right now..

So the conclusion is that there's no way to repel non-charged materials except with radiation pressure, eh? All right, then

Marcilla: "I have a job helping a guy who's head of the University of Washington's fusion project, but all I really know is enough to keep away from the equipment, and not to close doors that say not to close them."